This invention relates to trip or trigger type valve operators and in particular to trip type valve operators for actuating quarter turn valving, which are configurable for triggering in response to a variety of sensed conditions as might be needed, for instance, in a safety shutdown of a fluid handling system or emergency activation of safety equipment or hazard suppression equipment. The invention further relates to sensors, transducers and other trip actuators for use therewith and in particular is directed toward a seismic vibration sensor and transducer for detecting damaging earthquake ground motion.
A variety of trip or trigger type valve operators and valves or trip valves are known in the prior art. Such valve operators function by sensing some unsafe condition through some sensing means and then actuating a valve from its reset position to its returned position. The returned position is usually either the closed or opened position of the valve. Depending on the sensors and/or the transducers employed therein, trip type valve operators and their associated valves are known by an assortment of names such as manual reset valve, fusible link emergency shutoff valve, seismic sensitive valve, sprinkler valve, or just a safety valve to name a few. The terms trip and trigger will be used interchangeably.
More specifically, trip valves are used as automatic shutoffs, vents, diverters, etc. in fluid transport, processing and storage systems in order to deal with hazardous conditions such as pipe rupture, excess flow, extreme overpressure, improper startup or control sequence procedures, and fires which can result from equipment failure, control system malfunction, human operator error, accidents, and destructive natural phenomena. These hazardous conditions need to be dealt with quickly before further equipment failures and malfunctions result and in order to minimize possible subsequent additional hazards such as fires, explosions and releases of toxic substances which can lead to loss of life and property and to contamination of the environment. Trip type valve operators also are used as spring returned `failsafe` type valve operators where the controlled actuator (e.g. manual gearbox or electric gear motor) can not be return actuated by a spring return actuator.
The prior art teaches making trip valves in several ways. A few trip valves propose the use of standard valving such as ball valves or butterfly valves as their valve element while most prior art trip valves use specially designed valves which tend to be modifications of sliding stem globe or angle valves. Standard valves such as quarter turn ball valves and butterfly valves, have relatively high actuation loads whereas the common theme which runs through the special valve element designs is to find ways to reduce the valve actuation load so that the load is not such a problem to provide an actuator for and is not such a problem to trip. This typically involves either removing the usual valve stem packing or seals to reduce friction loads, or using the fluid pressure within the valve to actuate the valve closed and cause the valve plug to seal against the valve seats, or using only small valves which present smaller loads than larger valves, or limiting the maximum operating pressure of the valve to low pressures so that sealing requirements and hence friction loads therefrom are reduced and hydrostatic loads on the valve plug are reduced, or various combinations of these techniques. All of these techniques, however, have the serious drawback of compromising the basic utility and application versatility of the valve element. Such valve elements and their operators are, therefore, of limited use.
Quarter turn valving, such as ball valves and butterfly valves, has all of the following desirable features: high flow capacity and low pressure drops, ample to high pressure ratings, tight shutoff, a proven track record of relatively trouble free operation, stock availability in a variety of materials, stock availability with approval by recognized testing laboratories for a variety of services, economical, and generally speaking enjoys the wide acceptance of various industries, government departments and agencies, and building codes.
The few attempts in the prior art to apply a trip type valve operator to standard quarter turn valving all have various combinations of the following problems.
First, the spring actuators used in prior art trip type valve operators tend to be either impractically large or of questionable ability to meet typical quarter turn valve loads.
Second, the spring actuators used in prior art trip valve operators are not loadmatched to the typical quarter turn valve loads nor are the retensioning loads loadmatched to the reset actuator or controlled actuator and, therefore, are not used efficiently. All the consequences that this problem entails are described in my U.S. Pat. No. 4,869,459 of Sept. 26, 1989.
Third, is the problem of high trigger loads. Quarter turn valves present high loads (typical manufacturers' operating torque specifications for 1", 3", and 6" ball valves are 150, 600, and 3,000 IN.-LB. respectively) and therefore require high output actuators. If these high output actuators were indeed provided in prior art trip valve operators, then they would suffer from high trigger loads. The high trigger loads in turn can produce lock-up, high frictional loads and binding, or unintended triggering. On the other hand, mechanical sensing devices and other trip actuators such as solenoids typically will produce only a few ounces to a few pounds of trip actuating force because of the practical considerations of keeping these devices relatively small so that they can be compactly integrated into a product package and produced economically. Prior art devices do not take the limited sensor output and the high loads at the trigger into account.
Fourth, when the above second problem is considered in the light of the above third problem it will be seen that the second problem makes the third problem worse, in that the excess spring return actuator output at the reset position will directly result in higher force levels at the trigger with correspondingly higher loads for the sensors, transducers and/or trip actuators to overcome.
Fifth is the problem of large frictional torque arms within the tripping devices. Large frictional torque arms can cause a tripping device to bind, regardless of whether the loads therein are large or small. Associated with the problem of large frictional torque arms is the uncertainty surrounding the magnitude of static frictional forces. It will be noted that a static friction coefficient is not a precise design parameter. Repeated measurements of static friction coefficients between any two materials of a given surface finish typically produces a rather wide scatter in the data. Furthermore, effects such as wear, contamination, corrosion, and improper maintanence (i.e. such as never doing any maintanence resulting in the eventual disappearance or gumming or varnishing of the lubricants or perhaps putting lubricants on parts which should not have any lubricant) will lead to wide variations in the level of static frictional forces. Hence, any tripping device dependent upon a precise level of static frictional forces for proper operation, will in fact be subject to trip failure where the trip will not actuate when it is supposed to release the return actuator due to high-side variations in static friction or will lead to nuisance actuations where the trip actuates when it is supposed to continue to hold the return actuator due to low-side variations in static friction.
Sixth is the problem of compactness. The size of prior art trip type valve operators for quarter turn valves tend to be large in comparison to the size of the valve being controlled.
Seventh, many of the devices proposed in the prior art are not capable of a single action reset as might be accomplished manually with a simple lever handle or in a power assisted manner with for example a hydraulic cylinder. These prior art devices tend to require the manual reassembly and realignment of various arms and other parts thus making them difficult to use and perhaps inviting tampering with their internal workings.
Eighth is the problem of scaling up a trip valve operator so that it can operate larger sized valves without having to increase the trip actuating output and therefore size and cost of the sensors, transducers, and/or trip actuators. (Aside from size and cost, increases in sensor and transducer sizes can result in reduced sensitivity and slower response times.) The prior art, however, does not address or contemplate this scaling problem and a solution appears to be beyond its capabilities. My analysis of various valve manufacturer's operating torque specifications indicates that many make and models of intermediate to larger sized ball valves have operating torque requirements which scale approximately as the nominal valve size squared. In some series of smaller ball valves operating torque scales roughly with the valve size to the 1.3 to 1.5 power. At least one intermediate sized line of ball valves shows nearly a cubic relationship. In some butterfly valve series, operating torque scales approximately as the valve size squared while in some other series the operating torque scales approximately as the valve size cubed. In attempting to scale up prior art trip valve operators to accomodate larger sized valves where the valve operating torque is increasing as the second or third power of the valve size and also attempting to keep the trigger load constant so that the sensors and transducers and their trip actuating outputs can remain constant, one finds that prior art trip valve operators grow in size, and therefore weight and cost, so as to be completely out of proportion to the valves that they are intended to operate. Just taken alone, this problem indicates that prior art trip valve operators are, at best, impractical for application to anything more than the smallest valving.
It will be noted that the commercially available fusible link trip type valve operators for quarter turn valves have drawbacks in that, due to the above noted problems, other typical trip actuators such as a solenoid or a vibration sensor can not be substituted for the fusible link. Such a valve operator, therefore, lacks versatility. Also, these valve operators and the valves operated thereby are subjected to the same heat or fire which destroys the fusible link to cause triggering and can, therefore, be severely damaged by said heat or fire.
Some trip type valve operators in the prior art incorporate a simple toggle. Simple toggles have the property of providing mechanical advantage or leverage, thus reducing to some extent the load imposed on the tripping devices. Simple toggles, however, are subject to some debilitating tradeoffs. For a simple toggle to produce more leverage in order to reduce the trip or trigger load, the knee of the toggle must be brought closer to being straight. But, the straighter the knee of the toggle becomes, the lower the releasing forces and torques become. If the releasing torques are less than the frictionally induced holding torques, then the toggle binds and will not self release. My analysis of the friction effects in a simple toggle with some conservative assumptions about static friction coefficients (u=1), indicates that the knee pivot should remain at least two pivot radii from the straightened position in order to reliably self release when tripped, thereby limiting the leverage obtainable by straightening the toggle. Alternatively, increased leverage can be obtained from a toggle by increasing the length of the toggle links, but this is not desireable either because the size of the valve operator is increased, whereas compactness is generally sought. A further problem to the use of simple toggles in trip type valve operators is that simple toggles do not have the scaling properties to allow trip actuating sensors and transducers to trip progressively larger valve loads in a practically sized trip valve operator, as described above. Simple toggles in the prior art are used on sliding stem type valves and therefore, for a given pressure rating, valve load will scale as the valve size squared. For reasons of material strength, pivot shear area would have to scale with the valve load. If the toggle was scaled up in the same proportion as the valve size then the length of the toggle links would increase which would provide increased leverage, but the enlarged pivots also must be positioned further away from the straightened position (in order to provide a reliable self release when tripped) which would provide decreased leverage. The two opposing changes in leverage cancel out and the result is that as the toggle is scaled up, there is no increase in leverage. Hence, the trip actuating output and therefore the size and cost of the sensors and transducers would have to scale up as the valve size to the second power. Alternatively, if the sensors and transducers were not to be scaled up, then to reduce the trip actuating load, the length of the toggle links would have to be scaled up as the valve size cubed which is not desireable as, again, compactness is sought. Either way or splitting the scaling between the toggle size and the sensor trip actuating output, this scaling problem is a major limitation to the application of a simple toggle to trip valve operators. The above problems are made worse when the toggle is made to self lock rather than self release as the trip actuator, in order to produce triggering, has to do work against the friction in the toggle in order to actuate the toggle to a point where the toggle will self release.
Other trip type valve operators in the prior art incorporate disengageable arms and/or levers. These devices suffer variously from insufficient leverage, large operating area requirements, large frictional torque arms and consequent unreliable release from the reset position upon tripping, lack of a single action reset capability, and inability to scale up in proportion to the size of the valve and provide a trip load which does not increase.
Some trip type valve operators in the prior art are termed `free handle` manual reset valves and contain a solenoid trip actuator and a manually operated handle type reset actuator. Once tripped, the `free handle` effect causes the valve to be incapable of being reset until the condition which caused tripping is cleared. None of these are based on quarter turn valve technology.
Other trip type valve operators in the prior art are spring returned electric gear motor valve operators. The purpose of the spring return actuator is to provide a failsafe. In some of these valve operators, the electric gear motor actuator first retensions the spring return actuator and then actuates the valve rather than actuating both simultaneously. Some of these use large and costly arrangements of gears, splines, and leadscrews. Others have return actuators and tripping devices which must move as a mounted unit with respect to the valve thereby causing such valve operators to be about twice as large as valve operators where the return actuator and tripping device are mounted to a stationary frame and necessitating the movement of the control connections to the tripping device. Such movement can cause electrical wire type connections to eventually fail and can make the connection of many kinds of remote sensors through mechanical transmission means very difficult and impractical.
The need for seismic sensitive trip valves or just seismic valves is apparent. Fires and conflagrations resulting from earthquake shake damage have been known to be a cause of major property losses, sometimes many times larger than the direct shake damage. In the 1906 San Francisco Earthquake and Fire, the subsequent fires are reported to have caused as much as ten times the damage directly attributable to earthquake shaking. Leakage of flammable, explosive, and/or toxic fluids from broken piping and broken piping connections to various equipment significantly contributes to the fire and conflagration danger after a strong earthquake. Recent projections by seismologists, as reported in various scientific journals and news reports, indicate the likelihood of a magnitude 7.5-8+(Richter Scale) earthquake on the San Andreas Fault in Southern California within the next 30 years. Current estimates of property losses vary quite a bit, but tend to be in the 10 to 30 billion dollar range. Similar projections have been made for a magnitude 7-7.5 earthquake on the Hayward Fault near the San Francisco Bay Area. (It is interesting to note by comparison, however, that most estimates of damage due to the Loma Prieta earthquake of 10/17/89, magnitude 7.1, on the San Andreas Fault near Santa Cruz, but not particularly close to the Bay Area as a whole, have been put at 7 billion dollars.) If, however, numerous fires were to start and spread following these projected earthquakes, aided and abetted by leaking flammable or exposive fluids, and the fire fighting response were sufficiently hampered, as could be caused by broken water mains or leaking toxic fluids, then large fire and conflagration losses relative to the amount of shake damage would be possible, in which case the above loss estimates may well be low.
Experience in previous earthquakes (e.g. San Fernando 1971 and Whittier 1987) has shown that utilities, including natural gas pipes, water pipes, sewer pipes, and electrical lines, both those within buildings and those buried in the ground are subject to many breaks. Escaping natural gas is obviously an explosion and fire hazard and, in fact, numerous news reports of the Whittier 1987 quake indicated that there were about 65 natural gas fires just in the City of Los Angeles due to broken piping. Piping within chemical and hydrocarbon processing plants, airport fuel storage facilities, water treatment plants and sewerage treatment plants, to name a few, can also be broken as a result of strong ground motion with subsequent release of toxic gases (e.g. chlorine) and various explosive and flammable gases and liquids.
Manual shut-off of valves and switches is the currently planned method for dealing with the above situation. However, earthquakes give no warning and as yet are considered unpredictable in any relatively short time frame. Thus, no last minute emergency preparations, such as utility shut-offs, can be made. Further, most buildings are unoccupied or only lightly occupied during a substantial fraction of a day (businesses at night, residences during the day, often both on weekends). Hence, these important shut-offs will probably not be made in anything like a timely manner, thus increasing the chances of losses. If persons were in a particular building at the time of a strong quake, conceivably they could be injured or incapacitated and be unable to deal with the emergency. Lastly, there is always the chance of a panicked reaction during such situations. To put the matter plainly, any scheme for the manual securing of critical fluid lines during the emergency following a large or a great earthquake will be unreliable and invites enormous losses.
ANSI and the State of California have both issued standards determining minimum levels of acceptable construction and performance for seismic shutoff valves for natural gas service, ANSI Z21.70 and California Standard No. 12-23-1 respectively. In fact, the California standard is now state law. These standards call for a seismic shutoff valve to actuate when exposed to simple harmonic motion of 0.3 g amplitude at a period of 0.4 sec and not to actuate when exposed to simple harmonic motion of 0.4 g amplitude at a period of 0.1 sec, 0.08 g amplitude at a period of 0.4 sec, and 0.08 g amplitude at a period of 1.0 sec. It should be noted, however, that seismic ground motion is not simple harmonic motion.
Prior art seismic shutoff valves suffer from a number of various problems including the type of sensor used, the predictability of the sensor setpoint (not only when exposed to test stand simple harmonic motion but also when exposed to seismic motion), the sensitivity of the sensor to being out of level, and the ability of the sensor to generate sufficient force and displacement output to actuate a trigger. Additionally, prior art devices suffer from the problems of trip valve operators already noted and also encounter problems concerning the type of valving used.
Prior art devices use a variety of means for sensing ground vibration of which a ball or balls rolling or hopping over a lip seems to be the most common. Several problems tend to occur in these type of devices. First, the setpoint for triggering in response to horizontal earthquake ground motion can be interfered with by the vertical component of the earthquake ground motion. Second, the trip actuating output depends on the weight of the ball which for a relatively compact device will be small. Third, resetting a freely moveable ball requires either manual replacement of the ball (which is generally undesirable because the valve operator or valve must then be entered thereby increasing the chances for misuse, malfunction, and tampering) or the provisioning of extra mechanisms so that the ball may be restored to its seat. Fourth, small deviations from level will interfere with the setpoint.
A few prior art devices use sensing elements which are based on pendulums or on inverted pendulums. These devices also encounter problems. First, pendulums have a gravity based restoring force due to the arcuate nature of pendulum motion. Therefore, the response of a pendulum to horizontal seismic ground motion can be interfered with by the vertical component of the seismic ground motion thereby either degrading the accuracy of the triggering setpoint or making the triggering setpoint unpredictable. Second, pendulums tend to be rather long in vertical height which consequently causes the seismic sensitive trip valves into which they are integrated to not be particularly compact devices. It will be noted that attempting to impose size constraints on a pendulum type sensor undesireably affects basic setpoint parameters of the pendulum, as the length of the pendulum determines its natural frequency. Third, pendulums configured for sensing horizontal motion can not additionally function as a vertical motion sensor.
Problems are encountered by those attempts in the prior art to provide an inertia mass type sensor which is supported by bearing balls or rollers. In one such device, bearing balls are loosely located in sockets. Such bearings are likely to fail because no means are provided for retaining and aligning the bearing balls with respect to the inertia mass or supporting plane. It is to be expected that alignment would be lost after a few oscillations of the sensor. When a bearing ball reaches the edge of its socket it will stop rolling and start sliding with respect to the surfaces with which it is in contact thereby creating substantial friction. Also, if the valve is tipped or inverted, as is likely during shipping, handling, and installation, then the bearing balls will most likely come out their sockets, thereby producing bearing failure.
Most prior art seismic trip valves do not incorporate or have the ability to operate an industry standard valve, in particular a quarter turn ball valve or butterfly valve, which has high flow capacity, ample pressure ratings, tight shut-off, a proven track record of trouble free operation, and commercially available with ratings for use in various pertinent services such as natural gas, crude oil, gasoline, aircraft fuel, and chlorine and other toxic gases. Lack of such features in any safety valve would be a serious drawback to commercialization.